This invention generally relates to a multiconductor interconnect. More particularly, this invention relates to a space saving multiconductor interconnect for coupling two or more components of a particular device.
With increased computerization, more and more sensitive and valuable information is being generated and stored. Consequently, the need for high capacity and cost effective data storage is ever increasing. Dual and single reel tape drives have become a preferred method for storing electronic data.
Referring to FIG. 1, using linear recording technology, a tape drive pulls tape 10 across a transducer head 12 saving and/or retrieving electronic data in multiple parallel tracks that extend along the length of tape 10. Increasing the number of tracks on tape 10 and decreasing the space between each track increases the tape""s storage capacity. However, this also increases the complexity of head 12. Head 12 includes a number of read/write elements (not shown) formed on a thin film wafer 14. To align the read/write elements with a particular track on tape 10, head 12 may also include servo elements which read and possibly write alignment and position information on tape 10. The servo information can be used to accurately position head 12 both across the width of tape 10 on a desired track and along the length of tape 10 at the start of a specified file.
To enable a drive to read and write data while reading and recording alignment information, a number of traces 16 and corresponding bond pads 18 are required to connect head 12 to the other components of the tape drive. For example, an eight track head requires eighty or more traces. Additional traces for shield connections, ground lines, and connections on thin film wafer 14 can raise that total to ninety or more.
Typically, one or more ribbon cables 20 are used to connect head 12 to the other components of a tape drive. Ribbon cable 20 consists of a series of conductors 22 on a flat flexible strip of insulative material. Conductors 22, generally parallel to one another, extend along the length of the strip terminating at each end of the strip with bond pads 24 or some other suitable termination points. On one end of the strip, as shown in FIG. 1, each bond pad 24 on the ribbon cable is coupled to a corresponding bond pad 18 on thin film wafer 14 of head 12 with bond wires 26 using thermocompression, thermosonic, or ultrasonic wire bonding techniques. Bond pads 18 and 24 and bond wires 26 are then encapsulated in epoxy 28 or some other suitable encapsulating material.
Current technology allows placement of approximately 45 conductors on a 7 millimeter wide ribbon cable. However, the same number of traces require only a 3 millimeter width on thin film wafer 14. Referring still to FIG. 1, one known solution for aligning bond pads 24 on ribbon 20 with the bond pads 18 on thin film wafer 14 involves fanning out traces 16. This solution increases the size of thin film wafer 14 and, consequently, the manufacturing cost of transducer head 12.
Referring now to FIG. 2, instead of fanning out the traces on transducer head 12, a second known solution involves fanning out bond wires 26 that connect ribbon cable 20 to head 12. However, the increased length in the outer bond wires causes a number of problems. First, the longer wires are more likely to contact adjacent wires and cause a short circuit. It is difficult to adapt a wire bond tool to the changing angles of bond wires 26, and the longer outer wires are more likely to snag on the tooling and break before encapsulation. And, the additional length of the outer bond wires 26 increases the resistance and inductance of the connection between head 12 and the other components of a tape drive.
Referring now to FIG. 3A, a third known solution is revealed in U.S. Pat. No. 3,633,189 which issued to Shahbuddin Billawala in 1972. Billawala discloses a ribbon cable 20 capable of concentrating bond pads 24 into a small area. Ribbon cable 20 terminates on one end with a central portion 30 and two lateral portions 32. Transverse portions 34 connect each lateral portion 32 to the central portion 30. One half of ribbon cable""s conductors terminate with bond pads 24 on central portion 30 while one quarter of the conductors terminate with bond pads 24 on each lateral portion 32. FIG. 3B shows a slightly modified version of Billawala""s cable. Each transverse portion 34 is folded over itself placing the lateral portions 32 in a plane parallel to that of central portion 30. This places bond pads 24 in two parallel rowsxe2x80x94the first row defined on central portion 30 and the second row defined on lateral portions 32.
While Billawala allows ribbon cable 20 to be wire bonded to head 12 without fanning bond wires 26 or traces 16 on head 12, the design creates a number of problems. First, the unsupported folded transverse portions 34 increase the thickness of ribbon cable 20. The increased length of the conductors passing through transverse portions 34 increases the cable""s resistance and inductance. If each conductor has different electrical characteristics, balancing the tape drive""s amplifiers for the read elements and drivers for the write elements becomes more difficult. The loops in the conductors created by folding transverse portions 34 increase the cable""s susceptibility to magnetic interference. The double folds also increase the risk of broken conductors. Finally, wire bonding requires accurate placement of all bond pads 18 and 24, and Billawala fails to disclose a method for reliably aligning bond pads 28 on the lateral portions 32 with those on central portion 30 after lateral sections 34 are folded.
The present invention is directed to a space saving multiconductor interconnect. A plurality of conductors extend through the interconnect. To decrease the width of a selected portion of the interconnect, the conductors are split between two layers. One group the conductors extend along a portion of a first layer jumping to and continuing along a second layer. The remaining conductors extend only along the first layer. Consequently, the width of the interconnect where the conductors are split between the layers can be substantially reduced.
In one exemplary embodiment, the first layer is characterized by a first section having only first conductors and a second section having both the first second conductors. The first conductors in the first section of the first layer span a first width and the first and second conductors in the second section of the first layer span a second width greater than the first width. The second layer includes third conductors extending between first and second sections of the second layer. The third conductors in the first section of the second layer span a third width, and the third conductors in the second section of the second layer span a fourth width.